Double Rifle Regulation, Handloading and Other Topics relating to Double Rifles.

In answer to one query, I wrote the following. But it is worth repeating here and permanently attached to an image.

(image used is an image from buckstix)

Gunmaker Regulation
First regulation is done by the double rifle maker. The barrels are not yet fixed or soldered permanently in place. They are temporarily attached togethered and the maker will test shoot the rifle and adjust the barrels fit together until the bullets impacts "regulate" ie the different barrels impact closely together at the chosen distance. Then permanently affixed, ribs added etc.

The regulating gunmaker at Heym Gunmakers told me the European market prefers the method of the two barrels shooting parallel at the sighting distance. Americans prefer the bullet paths to cross. The parallel method is the correct one.

The Heym regulating gunsmith also uses a seven second delay between shooting the two barrels. The heat of the barrels will also affect the regulation impact. So shooting quicker will mean a hotter barrel(s) and shooting much slower will allow them to cool down more. Obviously there is some compromise in actual hunting use. The Heym shooting range has video cameras on the targets recording the bullet impacts so each barrel impact is precisely known.

The regulating is done with a specific ammunition brand, type of bullet, bullet weight, design, velocity etc.

Non fixed barrel double rifles
Some double rifles do not have fixed barrels. These are cheaper as a result. As it takes significant ammunition and time sometimes for an individual DR to be regulated by the maker. These DRs without fixed barrels usually have wedges in between the barrels. Held in place by small screws. Moving the wedges will change the angle of the barrels to each other or laterally or vertically - depending on whether a SS or UO - and change the bullet impact of each barrel. Again the owner can self regulate the barrels for the load or ammunition they wish to use. Examples are the Valmet/Tikka/Finnclassic U&O double rifles. I have one such DR with a few barrel sets.

Some DR brands are crap and do not regulate their DRs at all. A reason these brands are so much cheaper.

Regulating barrels is not rocket science. On the nitroexpress.com forums we have ordinary members, skilled of course, who have removed the solder from their own DRs and re-regulated them, properly, and re-soldered them again. Not within my personal skill set though!

Which trigger and barrel first?
Usually it is proper to shoot the first trigger or right barrel on a side by side first to obtain proper regulation. And then the rear trigger and left barrel. Some will insist this is the ONLY way. However, some drs will still shoot to regulation using the left barrel and rear trigger first. No way to know, give your rifle a try and see how it performs.

For under and overs, an U/O shotgun usually will shoot the lower barrel first with the front trigger. My Tikka/Valmet shoots the top barrel first. IMO this makes sense. As the sights will more closely relate to the top barrel. And the result more accuate longer range shooting. Also secondly as this double rifle also has combination barrels, with the shotgun barrel being on top, it is usual for a combination to have the shotgun barrel firing first. It originally had a single trigger, with a selector. I had it changed to double triggers.

Some DRs will shoot either barrel first OK, and for double triggers and heavy recoiling rifles using the rear trigger will mean the shooter does not slap the rear trigger on recoil and fire it if using the front trigger first. More users of DR "double fire" by mistake than will admit it. I have done it myself, including on a cow elephant hunt. Sometimes a double rifle will malfunction. I had a SINGLE trigger DR shoot both barrels off at once on recoil at a gunmakers shooting event, borrowing one of their rifles. So no user trigger mistake there. The correct method of trigger pull is to use the first trigger first and curl ones trigger finger in and not use a finger tip only. All of my double rifles and two barrelled shotguns, about fifteen in total are all double trigger firearms.

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Handloading a duplication regulation load
With handloading, what is often referred to as "regulation" is duplicating a regulation load. As previously said, the DR was originally regulated with a specific ammunition load. Overtime the ammo might change, become unavailable, or the rifle change its response, for whatever reason. For example one big change was the change of propellant from black powder to cordite sticks, and then to smokeless powders. This may have affected regulation especially for older DRs. Often simply the old Kynoch ammo is not available at all. The owner may also want to shoot their own handloads. Far cheaper than buying factory ammunition

So the DR handloader will try to duplicate the orginal regulation ammo load or find a recipe which shoots to regulation. They may want to use a different bullet weight.

Bullets
Regarding bullets, Woodleigh Bullets designed a lot of their bullets with the same shape and weights as original Kynoch NE ammo. Specially for regulation duplication. So a 480 gr .450/458 Woodweigh Weldcare SP or FMJ has a shape similar to the orginal NE bullet for a .450 NE double rifle.

Avoid Monometal bullets
Avoid the use of monometal bullets without raised driving bands in thin walled double rifles. These may damage your rifle. The raised driving bands may allow the engraving by the rifling to be done on such a monometal bullet without undue pressure on the barrels. Without the raised driving bands, the barrels may be damaged by the monometal bullet as there may not be enough give in the solid bullet for the rifling to engrave into properly.

The DR handloader will choose a bullet. An appropriate powder, case and primer and load and shoot the rifle appropriately for both accuracy and impact of the barrels and how close together/ Adjusting the velocity to bring the barrels together or wider apart depending on whether the impacts have already crossed. Using different powder charges to decrease or increase the velocity.

The "75% Rule"
Now some DRs will shoot to regulation more than one bullet weight. Some owners of DRs claim there is a "75% rule". That one can use a bullet 75% of the usual weight, at the same velocity and the DR will shoot it OK. For example, a 350gr projectile instead of a 480 gr projectile in a .450. Or a 300 gr instead of a 400 gr in a .400. Only way to find out for your specific DR is to try it and see.

Pressure in a break open firearm
Velocity and pressure. Use a chronograph. Do not exceed the velocities the original ammo was loaded to, or not by much. If your NE cartridge was originally loaded to 2150 fps for say a 480 gr bullet, that is the guide to use. If looking for the usual bolt action case excess pressure signs in a break open firearm, you will probably be well exceeding the safe pressures by the time you see such pressure signs. Break open firearms have usually a lower tolerance for pressure.

Bullet impact changes at the target
Note, regarding regulation bullet impact. A slow heavy bullet may travel for a while in a recoiling barrel before exiting, so the impact for a faster velocity load may actually drop the impact on the target. Usually for high velocity rifles, there is less drop, ie a flatter trajectry, so the actual result for an NE cartridge may be the opposite.

Also there may be cross wise travel on recoil before the bullet exits, two barrels forming something of a X. One barrel moving upwards and bit more to the left, the other moving up and a bit more to the right. Possible minor differences in bullet impact. We want them exiting the barrels in such a way that the bullets are parallel at the prime target distance.

Holding the double rifle
How the dr is held is also important. Do not use a rest with the rifle resting on the sandbags. Put the butt into your shoulder and rest your forehand hand on the bags, holding rifle. Heavy recoiling rifles are also best shot from a standing rest, not a sitting bench. For comfort reasons.

Sights and regulation
Sights. A DR regulated for open sights may shoot differently if a scope is added. The difference in weight and balance may affect the regulation. If ordering a factory made DR, you would specify which scope you want on it, and it will be regulated with it in place. How it will shoot then with only open sights? Only trial and error will tell. It might be fine, it might not be. Usually the bigger bore double rifles, certainly .450s and bigger are not scoped. So would be regulated for open wide V sights. Some might put small electronic dot point sights on them however. Especially for ageing eyes. IMO the heaver and more bulky a sight or scope is, the more likely regulation and bullet impact will be affected.

Re-regulating a double rifle
Sometimes a different bullet, powder, primer or brass case makes a difference in regulation. Sometimes getting the barrels properly re-regulated is the only solution, having them separated, test shot and regulated and resoldered by a competent DR gunsmith/maker.

All sounds complicated but usually is not that difficult to find something usable. Especially new rifles, where loaded ammo used in regulating may still be available. And the actual details of the regulation discoverable. For handloads it is a method of trial and error, starting from an intelligent base.

"Minute of buffalo" vs Fine Accuracy
Big bore double rifles are often said to shoot to "minute of buffalo", ie the two barrel, say four round groups are several inches in size at 50 yards or 100 yards. In the end if hunting buffalo, the chest killing area is not small, and fine accuracy is not needed, unless one wishes to snipe a buffalo from long distance. A DR is ideal for buffalo or other bovines at usual hunting distances and especially close range. An elephant's brain is small, American football sized. But elephants are hunted nice and very close, 10 to 25 yards.

HOWEVER a double rifle may be very accurate. My Tikka 512SD U/O dr in 9.3x74R will put four rounds, each barrel with the two bullet holes touching the upper and lower barrels impact one inch apart at 100 yards. I regulated this dr that way with its movable barrels. Very accurate. In theory I could shoot this DR to reasonable longer hunting ranges. I also have used a Frankonia U/O in .22 Magnum and 5.6x50R, two difference cartridge chamberings, where the 5.6x50R barrel shot 5 shot one hole groups at 100 metres. The .22 Mag only 30 mm groups at the same. But an inch or two higher. So a DR need not be unduly inaccurate.

Accuracy on heavy recoiling firearms is often influenced by shooter error. No one likes recoil. It is harder to shoot to the same accuracy a .458 Lott as a .223. Flinching, unconscious extreme flinching can result in complete misses. If this starts for you, try to correct it. You may not know it is occurring until you accidently pull the trigger on an empty chamber. I find when doing range sessions, swapping froma heavy recoiling rifle to a mild one, a .450 to even a .375 which still kicks, or a .303, makes a big difference.

Swap back up after a while. A good idea is to limit the number of painful recoiling shots one fires in a session as well.

Some may mention using a single barrel well sighted and known for longer range shooting. I agree with this concept. If one knows the impact of say the first barrel at 50 yards, 100 yards, 150 yards and 200 yards, and the rifle is shot as a single shot, why not? Great if the second barrel impacts similarly. But one barrel can at least be used accurately. If an animal shot at, subsequentally runs away, how important is the accuracy and close regulation of the second barrel? If at 200 yards and it hits six inches apart, does it matter on a buffalo running away? Can you shoot that fine on a running beast with a bolt action? Most can't.

Summary
Regulation is an important part of a double rifle. Both barrels should shoot reasonably close together at shorter to medium hunting ranges.

The above is from my personal experience, use of DRs since first in 1983, but mostly the last twenty years or so, my academic knowledge, from very knowledgeable friends and gunmaker acquaintances, and from running a double rifle forum for twenty years. Not all with agree with all the comments.